


TN295 
.U4 

No. 9173 



LIBRARY OF CONGRESS 



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Bureau of Mines Information Circular/1988 




Investigation of Dust Sources and Control 
Technology for Longwall Plow Operations 

By John J. McClelland and Robert A. Jankowski 



UNITED STATES DEPARTMENT OF THE INTERIOR 




Information Circular 9173 



Investigation of Dust Sources and Control 
Technology for Longwall Plow Operations 

By John J. McClelland and Robert A. Jankowski 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 

David S. Brown, Acting Director 



TUaqs 
i 

73 



Library of Congress Cataloging in Publication Data: 



McClelland, John J. 








Investigation of dust sources 


and control technology for longwall plow 


operations. 








(Bureau of Mines information circular 


; 9173) 






Bibliography: p. 10 








Supt. of Docs, no.: I 28.27: 9173. 








1. Mine dusts. 2. Longwall mining. I 


Jankowski, Robert A. II. Title. 


III. Series: Infor- 


mation circular (United States. Bureau of Mines) 


; 9173. 




-?N39&.e4- [TN312] 




622 s [622 '.8] 


87-600333 



CONTENTS 



Page 



Abstract 1 

Introduction 2 

Test setup 3 

In situ conditions 3 

Sampling strategy 4 

Survey Results 5 

Discussion 7 

Conclusions 9 

References 10 

ILLUSTRATIONS 

1. Longwall plow face 2 

2. Typical respirable dust sources 5 

3. Instantaneous roof support dust concentrations at mine B 6 

4. Instantaneous dust concentrations by a plow at mine C 6 

5. Enclosed stageloader-crusher with strategic location of water sprays....... 8 

TABLES 

1. Principal operating parameters 3 

2. Gravimetric results 5 







UNIT OF MEASURE ABBREVIATIONS USED 


IN THIS REPORT 




cfm 


cubic foot per minute 


mg/m 3 


milligram per cubic meter 




ft 


foot 


min 


minute 




f t/min 


foot per minute 


pet 


percent 




gpm 


gallon per minute 


psi 


pound per square inch 




h 


hour 


s 


second 




in 


inch 







INVESTIGATION OF DUST SOURCES AND CONTROL TECHNOLOGY FOR 

LONGWALL PLOW OPERATIONS 

By John J. McClelland 1 and Robert A. Jankowski 2 



ABSTRACT 

The Bureau of Mines conducted a study of longwall plow operations to 
identify dust sources and existing control technology. Three longwalls 
employing either the high-speed overtaking or conventional method 
of mining were surveyed. Principal operating parameters and on-site 
dust control technology at the time of each survey are described. 
Short-term gravimetric and instantaneous sampling results are discussed 
in detail. The relationship between longwall dust levels and dust 
control technology was examined. 



'Mining engineer. 
Supervisory physical scientist. 
Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



The plow is a continuous mining machine 
equipped with a static set of cutting 
bits, positioned at a predetermined depth 
and height, for mining in both directions 
along a longwall face. The plow is 
pulled in either direction by a heavy- 
duty chain. The broken coal is loaded 
onto an armored flexible face conveyor 
which, with the aid of hydraulic rams, 
holds the plow to the coal face, thereby 
causing the bits to bite into the coal as 
they are pulled along it (fig. 1). 

Coal plows were initially developed in 
the Federal Republic of Germany (FRG) in 
the 1940' s for mining friable coal seams 
less than 4.3 ft thick (O. 3 At the 
present time, they are used on 50 pet of 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



the longwalls in the FRG ( 2_) . The first 
application of coal plow on a longwall 
face in the United States was in 1951 at 
a southern West Virginia coal mine (3_). 
The growth of plows in the U.S. coal 
market has been limited by advances in 
thin-seam shearer technology. Today, 
plow longwalls represent a small percent- 
age of U.S. longwalls and are primarily 
located in the Appalachian coal fields. 

Two mining methods are commonly 
employed in longwall plow operations: 

(1) the conventional method, which uses a 
plow speed of less than 125 ft/min, and 

(2) the high-speed overtaking method, 
which uses a plow speed of more than 300 
ft/min. With the conventional method, 
the plow runs more slowly than the con- 
veyor. This method is usually used in 
thick-coal seams, where the faster 
conveyor clears the larger product more 




FIGURE 1 .—Longwall plow face. 



easily. With the high-speed overtaking 
method, the plow travels much faster than 
the conveyor. This method is generally 
used for seams less than 42-in thick 
because of the high output potential. 
Uniform loading of the face conveyor is 
achieved by maintaining an optimum speed 
differential of 2: 1 to 3: 1 between the 
plow and conveyor (4). 

Plows are generally considered to pro- 
duce less dust than shearers since the 
plow's method of attack produces a larger 
product (5). However, it is also con- 
sidered more difficult to control these 
lower dust levels. A variety of control 
techniques are available to the operator. 
A sequentially activated spray system 
mounted on a face conveyor is the most 
popular and widely employed control tech- 
nique. Its purpose is to suppress dust 
in the vicinity of the plow; it does this 
by operating several groups of water 
sprays ahead of and behind the plow. 
Another technique of interest is a hose- 
handling, plow-mounted water-spray system 
that has been tried repeatedly, but 
with only limited success (6). Severe 



operational problems are often en- 
countered with the trailing water hose. 
These problems far outweigh the marginal 
improvements in dust reductions. Water 
infusion, whereby water is injected into 
the coal ahead of the face, can be a 
beneficial supplement to existing conven- 
tional dust control methods (7). How- 
ever, costs and coal seam infusibility 
often dictate whether it is a viable 
option. 

The Bureau of Mines began investigating 
plow operations when a longwall census 
indicated that average respirable dust 
levels for the designated occupations 
exceeded the 2.0-mg/m dust standard. In 
addition, a background literature search 
revealed that virtually no work has been 
done on plow operations in recent years. 

This report presents the results of 
three underground studies of both high- 
speed overtaking and conventional plow 
operations. The purpose of each survey 
was to identify and report on dust 
sources and existing longwall control 
technology. 



TEST SETUP 



IN SITU CONDITIONS 

Three mines were surveyed to identify 
dust sources and control technology on 



conventional and high-speed overtaking 
plow operations. The principal operating 
parameters for the mines surveyed are 
shown in table 1. 



TABLE 1. - Principal operating parameters 



Operating parameters 

Plowing method 

Plow speed ft/min. 

Conveyor speed. .. .ft/min. 

Depth of cut in. 

Seam 

Seam height in. 

Face length f t . 

Overburden f t . 

Moisture content pet . 

Water infused 

Hardgrove index 

Average face air 

velocity ft/min. 

Roof composition 

Floor composition 



Mine A 

Conventional 

132 

274 

4 

Pocahontas No. 3. 

48 , 

548 

600-900 

1.47 

No 

>100 , 

570 , 

Shale , 

Shale if 



Mine B 

High speed 

354 

181 

3-8 

Beckley 

46 

482 

900-1,000 

5.76 

No 

85 

560 , 

Shale to slate.. 

Slate with coal 
laminations. 



Mine C 



High speed. 

356. 

193. 

2-3. 

Lower Freeport. 

45. 

600. 

450. 

1.4. 

No. 

84. 

370. 

Shale with occa- 
sional sandstone. 
Clay. 



The following briefly describes the 
on-site application of existing control 
technology: 

Mine A : The primary means of con- 
trolling dust along the face was a manu- 
ally operated, constant fullface water- 
spray system. Twenty-seven spray blocks 
were mounted along the face conveyor 
spillplate at 20-ft intervals. Each 
block consisted of one nozzle operating 
at 100 psi. A crusher, mounted on the 
face conveyor located upwind of support 
15, was equipped with three nozzles 
on its intake side. Two sets of 10 flat- 
fan water-sprays were mounted at the 
f ace-conveyor-to-stageloader and stage- 
loader-to-belt transfer points that con- 
trolled dust in the headgate area (one 
set of sprays at each transfer point). 
The transfer-point sprays were enclosed 
with brattice. Observations revealed 
that very few transfer-point water sprays 
worked. A Wendon 4 wetting agent was used 
extensively throughout the section. 

Mine B : An electromechanically acti- 
vated sequential water-spray system was 
the primary means for controlling dust 
along the face. Ninety-six spray blocks, 
mounted at 5-ft intervals along the face 
conveyor spillplate, were sequentially 
activated in groups of 12 by electric 
solenoids. As the plow moved along the 
face, one group of sprays closed while 
the preceding group opened, thus keeping 
the plow enveloped with water at all 
times. Each spray block contained one 
nozzle of the adjustable flat-fan type, 
operating at 30 psi. Because the water 
sprays were the adjustable type, orienta- 
tion within a spray block was random. 
Cone sprays operating at 85 psi were used 
to control dust at transfer points. One 
set of two sprays was mounted at the face 
conveyor-to-stageloader transfer point, 
and one set of two sprays was mounted at 
the stageloader-to-belt transfer point. 
It was observed that stageloader-to-belt 

^Reference to specific equipment does 
not imply endorsement by the Bureau of 
Mines. 



water sprays were clogged and no sprays 
were used at the crusher. 

Mine C : A sequential water spray sys- 
tem, similar to mine B's system, was used 
to control dust along the face. Twelve 
groups of 10 spray blocks were sequen- 
tially activated by electric solenoids. 
Spray blocks were mounted at 5 ft inter- 
vals along the face conveyor spillplate. 
As part of a separate ongoing evaluation 
by the mine, three types of water sprays 
were used along the face: (1) atomizing, 
(2) 1/16-in jet, and (3) 3/32-in jet 
sprays. Each block contained 3 nozzles 
of the various types, with each nozzle 
operating at 160 psi. Spray blocks were 
oriented downwind, with spray coverage 
over the conveyor and lower third of the 
face. Eighteen water sprays, operating 
at 25 psi, were used to control dust in 
the headgate area. Sets of six water 
sprays were mounted, near the f ace-con- 
veyor-to-stageloader transfer point, at 
the stageloader-to-belt transfer point, 
and on the intake side of the stage- 
loader-mounted crusher. Brattice was 
used to cover portions of the stageloader 
and belting was used to enclose 
the crusher and crusher-mounted sprays. 
Because of poor headgate roof conditions, 
observations revealed that the crusher 
would frequently produce high concentra- 
tions of dust while handling the fallen 
roof rock. 

SAMPLING STRATEGY 

Instantaneous and short-term gravi- 
metric sampling methods were used to 
isolate and quantify potential sources of 
respirable dust. 

Four gravimetric sampling stations were 
identified along the headgate and face. 
Sets of two gravimetric samplers each 
were stationed in the last open crosscut, 
at two headgate locations (approximately 
at shields 3 and 15), and at the tailgate 
(about 15 shields from the tail entry). 
Face-side gravimetrics were suspended 
from roof support canopies over the walk- 
way. Eight gravimetric samplers were 
used as part of each day's sampling. No 



8-h, full-shift sampling similar to 
compliance sampling was performed. 

A MIE RAM-1 instantaneous dust monitor 
was used to measure dust concentrations 
generated by the plow and roof support 
movements. RAM-] data are normally re- 
corded on handheld audio tape recorders. 
After the survey of mine A, tape re- 
corders were replaced with Mine Safety 
and Health Administration (MSHA) approved 
solid-state digital data loggers. Each 
logger was preprogrammed to record one 
output voltage level from the RAM-1 every 
second, for a total run time of 34 min« 
The 1-s averaging and recording of output 
voltage insured accurate and consistent 
monitoring of dust levels at each sam- 
pling station. A portable microcomputer, 
in combination with communication soft- 
ware, was later used to retrieve and 
store logger data onto floppy disks for 
future analysis. 



Stationary instantaneous sampling was 
conducted at locations upwind of support 
35 during each survey. Earlier attempts 
to sample near the tailgate were unsuc- 
cessful because concurrent upwind activi- 
ties produced unpredictable background 
dust levels. By selecting two sampling 
locations in close proximity and upwind 
of support 35, it was possible to over- 
come restricted visibility and conduct 
accurately timed surveys of upwind and 
downwind face activity. Time study re- 
sults were used to interpret logger data 
by identifying events that may have had 
an adverse effect on dust levels. For 
example, it was important to make note of 
the start and stop times of the plow, 
face conveyor, and support movement acti- 
vity; changes in cut direction; and the 
location of the plow with respect to each 
sampling location. 



SURVEY RESULTS 



Gravimetric results are shown in ta- 
ble 2 and figure 2. Table 2 presents the 
average concentration measured at each 
sampling station for all three mines sur- 
veyed. Based on this information, 
respirable dust sources have been identi- 
fied and their contributions to face 
workers' exposure computed. Respirable 
dust sources fall into three groups: 
(1) sources that occur outby and repre- 
sent section intake dust, (2) sources up- 
wind of support 15 (specifically stage- 
loader and crusher-generated dust), and 
(3) sources that occur along the face 

TABLE 2. - Gravimetric results: 
average dust concentrations 1 in 
milligrams per cubic meter 



Sampling station 


Mine A 


Mine B z 


Mine C 


Section intake.. 


0.2 


0.5 


0.1 




1.1 


2.5 


1.3 




2.1 


2.4 


1.3 


Support 










3.1 


NA 


2.4 



NA Not available. 

Concentrations are 
equivalents. 

Data has been 
production. 



not calculated MRE 



normalized 



for 



(namely coal transport-, plow-, and 
support-generated dust). Figure 2 illus- 
trates the significance or insignificance 



Section intake (7.1 pet) 




Coal transport 
Plow 



_ 39.3 



Support movements J pct 

FIGURE 2.— Typical respirable dust sources. 



of each group based on the survey average 
of source contributions. 

Instantaneous sampling was conducted to 
identify the significance of group 3 dust 
sources. Individual segments of recorded 
instantaneous data were analyzed to iden- 
tify source contributions from plow 
and roof support movements. Current sam- 
pling methodologies did not permit inde- 
pendent evaluation of coal transport 
dust. Figures 3 and 4 represent typical 
time history plots of instantaneous dust 
levels for mines B and C, respectively. 



Figure 3 shows the significance of sup- 
port movements for face dust levels; fig- 
ure 4 presents dust levels measured near 
the plow. 



Mine A: 



Gravimetric results showed 



that the most significant change in dust 
levels occurred upwind of support 15. 
Sixty-eight percent, or 2. 1 mg/m 3 of 
respirable dust along the face, was 
measured at this location. Approximately 
0. 9 mg/m 3 was generated by the stage- 
loader upwind of support 3 and 1. mg/m 3 



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ESS Dust from support 
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TIME, min 

FIGURE 3.— Instantaneous roof support dust concentrations at mine B. 



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Dust plume 



KEY 
Plow passes sampler location 
during head-to-midface cut 




4 5 6 
TIME, min 

FIGURE 4.— Instantaneous dust concentrations by a plow at mine C. 



by a crusher mounted on the face conveyor 
upwind of support 15. Coal transport, 
the plow, and roof support movements gen- 
erated 1.0 mg/ra of dust along the face 
as measured at the tailgate support. 

Plow-generated dust is identified as 
the computed difference between dust lev- 
els measured on the intake and return-air 
sides of the plow. Instantaneous results 
indicated that plowing generates, on 
average, less than 0.2 RAM^ units of 
dust, regardless of cut direction. 

Concentrations measured downwind of two 
support operators were averaged, and 
intake levels subtracted to identify dust 
contributions from support movements. 
Roof support movements generated 1.8 RAM 
units of dust, with peak concentrations 
as high as 37.2 RAM units. 

Mine B ; Once again, a significant 
amount of dust was generated at the head- 
gate by the stageloader-crusher. Based 
on available gravimetric data, results 
showed that 2.0 mg/m of respirable dust 
was generated inby the last open cross- 
cut and upwind of support 3. This is a 
significant contribution by any measure. 
Because of equipment malfunctions, gravi- 
metric data are not available for the 
tailgate sampling location. 

Figure 3 shows a typical time history 
profile of instantaneous dust levels 
before and after the start of upwind sup- 
port movements. Best estimates are that 
support movements generated an average 
of 1.4 RAM units of dust. Figure 3 
also illustrates the insignificance of 



plow-generated dust. During the first 
4-1/2 min of sampling, and before the 
start of upwind support movements, there 
was virtually no measurable change in 
dust levels, despite the fact that the 
plow made two complete passes of the face 
(a pass equals one cut from head to tail 
plus one cut from tail to head). 

Mine C ; Results from this survey were 
essentially the same as the first two 
surveys. Forty-six pet of the respir- 
able dust along the face (1.2 mg/m 3 ) 
was generated upwind of support 3 by 
the stageloader-crusher. An additional 
46 pet was generated along the face (as 
measured at the tailgate support) by coal 
transport, plowing, and roof support 
movements. 

Figure 4 shows a typical profile of 
instantaneous dust levels measured while 
a plow was mining in the vicinity of the 
stationary sampling location. Unlike 
plows in the other mines surveyed, this 
plow was found to produce a measurable 
difference in respirable dust levels. 
During the head-to-midface cut, a plume 
of dust was observed traveling with and 
on the intake air side of the plow. At 
times, dust levels reached instantaneous 
peaks of 7.0 RAM units. Since dust is 
generated in only one cut direction and 
exposure to this dust is of short dura- 
tion, it is safe to assume that the plow 
was an insignificant dust source. Sup- 
port dust was generally found to be 
insignificant, except where clay veins 
were present. 



DISCUSSION 



Instantaneous and short-term gravi- 
metric sampling methods were used to 
identify respirable dust sources along 
high-speed overtaking and conventional 
plow operations. Gravimetric results 
provided information on three dust source 

C ; — 

-"A RAM unit is the relative numerical 
output from the RAM-1 and approximates 
respirable dust levels in milligrams per 
cubic meter. 



groups: section intake; stageloader- 
crusher; and coal transport, plow, and 
support movements. Instantaneous results 
helped to identify the significance of 
plow- and support-generated dust. 

The impact of a dust source on face 
workers' exposure is directly related to 
its frequency of occurrence (or time 
fraction of the mining cycle) and to the 
workers' location along the plow face, 
with respect to the dust source. For 



example, a stageloader- crusher operates 
100 pet of the actual mining time, and 
regardless of the operators' location 
along the face, they are exposed to this 
dust source 100 pet of the time. On the 
other hand, upwind support movements 
occur only 25 to 50 pet of the mining 
time. Although exposure to this dust 
source is less frequent, a tailgate 
worker on a plow face is exposed to many 
more upwind roof support movements than a 
worker located near the headgate. Theo- 
retically, dust exposure levels for the 
tailgate worker should be higher. The 
logic is the same for exposure to plow- 
generated dust as it is for exposure to 
support dust; the longer a worker stays 
on the return air side of a plow, the 
greater the exposure. 

On the longwall plow faces surveyed by 
the Bureau, the stageloader-crusher was 
found to be the most common and signifi- 
cant source of dust. Typically, 54 pet 
of the dust responsible for face worker 
exposure comes from the stageloader- 
crusher. Despite the mines' efforts to 
control this dust source, existing con- 
trol systems were inadequate. 

A number of low-cost alternatives are 
available for controlling stageloader- 
crusher dust. Strategically located 



water sprays mounted on an enclosed 
stageloader-crusher, or a water-powered 
scrubber that cleans the air inside it, 
can be very effective in reducing dust 
levels. An enclosed stageloader-crusher 
spray system consisting of twelve hollow- 
cone sprays (20 gpm total water flow) lo- 
cated in the crusher, at the intake and 
discharge side of the crusher, and im- 
mediately after the stageloader dump 
point, can reduce dust concentrations by 
74 pet at the stageloader (fig. 5) (8). 
A water-powered scrubber mounted on a 
stageloader and supplied with approxi- 
mately 9 gpm water at 500 psi, for an 
airflow of approximately 2,000 cfm, can 
reduce intake dust along the face by 
50 pet (JJ). Although a water-powered 
scrubber offers excellent dust control, 
its application to plow operations may be 
limited by seam height. 

Plow, coal transport, and support move- 
ments typically account for 38 pet of the 
dust responsible for face workers' 
exposure. Support-generated dust was a 
problem at mines A and B. Support dust 
problems normally occur when coal or 
some other highly friable roof material 
is ground and crushed during the advance 
and setting of roof supports (10). At 
mine A, the problem was a combination of 



Conveyor belt 



Crusher 
sprays 

Brattice hood 

Crusher intake 
sprays 




FIGURE 5.— Enclosed stageloader-crusher with strategic location of water sprays. 



poor roof conditions and failure of the 
uncut coal to fall freely away from the 
roof. At mine B, the problem was pri- 
marily roof coal. The solution to this 
problem is not quite clear. For plow 
operations, it is common and often neces- 
sary to mine at a cutting height that is 
lower than the seam height, to prevent 
the plow from riding into the roof and 
interrupting production. However, if the 
remaining uncut coal fails to break and 
fall freely away from the roof prior to 
the movement of supports, it can create a 
dust problem. Alternatives may include 
adjusting the cutting height, at the risk 
of interrupting production, or to intro- 
duce modified support-setting techniques. 
Attempts have been made to attach water 
sprays to roof support canopies and to 



wet the zone ahead of the support along 
the roof. Maintenance often becomes a 
problem, and it is usually difficult to 
prevent the sprays from being torn off. 

Finally, plow-generated dust does not 
present much of a problem. Only at 
mine C was a measurable change in dust 
levels observed. Since face personnel do 
not travel with the plow, unlike shearer 
operators who remain with the machine 
at all times, exposure to a short- 
duration dust cloud is insignificant. 
(For mine C, exposure normally did not 
last longer than 30 seconds for every 
other cut). This suggests that existing 
dust control technology is doing an ex- 
cellent job of controlling plow-generated 
dust, or that the plow produces very lit- 
tle dust in the respirable size range. 



CONCLUSIONS 



The stageloader-crusher is a primary 
source of dust on longwall plow opera- 
tions. Stageloader-crushers can generate 
over 60 pet of the dust along the face. 
The mines surveyed had all made attempts 
to control this dust source, but had met 
with little success. Implementation of 
stageloader-crusher control techniques 
means strategically locating water sprays 
under the brattice of an enclosed stage- 
loader, or mounting a water-powered 
scrubber to clean the air inside the 
machine. Either technique is relatively 
inexpensive and with proper maintenance 
can produce significant dust reductions. 

Support-generated dust presents a dust 
control problem when uncut coal fails to 
fall freely from the roof before advance- 
ment of the supports. The residual roof 
coal is crushed by roof support move- 
ments, possibly producing high concentra- 
tions of dust. This can be a serious 
problem for many workers who must remain 
at stationary locations along the plow 
face. Since dust exposure is a function 
of worker location along the face rela- 
tive to the dust source, a tailgate sup- 
port operator is exposed to many more 



upwind roof support movements than is 
a headgate operator, and theoretically 
should be exposed to higher dust levels. 
Two of the three mines surveyed had sup- 
port dust problems. The solution to con- 
trolling this dust source remains un- 
clear. It may prove more cost-effective 
to pursue control techniques for other 
more significant sources of dust, speci- 
fically the stageloader-crusher. 

Surprisingly, plow-generated dust was 
found to be insignificant. This suggests 
that existing control technology, in the 
form of constant or sequentially acti- 
vated face-conveyor-mounted water sprays, 
is adequate. Each system has its advan- 
tages. A sequential system optimizes the 
use of water by minimizing water flow and 
maximizing water pressure in the vicinity 
of the plow. It also reduces the amount 
of nuisance water, in the form of mist 
and runoff. On the other hand, a con- 
stant full-face system would ensure 
better saturation of the coal by wetting 
the coal well in advance of the cut and 
maintaining this saturated state during 
coal transport. 



10 



REFERENCES 



1. Olson, J. J. , and S. Tandanand. 
Mechanized Longwall Mining. A Review 
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